Introduction: Omental cysts are rare intra-abdominal lesions, with a frequency of 1:250,000, which often present asymptomatically. However, they can cause abdominal distension, or even surgical abdominal symptoms. Case report: A 3-year-old female patient presents with a clinical picture of 2 years of evolution, reporting progressive abdominal distention since she was one year old and abdominal pain for 2 weeks. Physical findings show an abdomen with great abdominal distention, tense and painful on superficial and deep palpation. A contrast-enhanced CT scan of the abdomen and pelvis revealed abdominopelvic cystic lesions. Exploratory laparotomy revealed a giant multilocular cystic mass dependent on the greater omentum. The pathological report revealed a giant omentum cyst. A successful surgical resection of the cystic lesions was performed and a favorable post-surgical evolution was performed. Conclusions: Omentum cysts are rare in paediatrics. Diagnosis is based on imaging studies and is confirmed during surgery. Surgical treatment is effective and with few complications